The blown film technique is an important means by which polyethylene films are manufactured. A major use of such films is in making bags, where the films can be formed as continuous cylinders then crimped to close one end. The process to blow polyethylenes into such films however is complex, requiring a balance between processability (flowability and melt strength) on the one hand and mechanical properties (e.g., Tensile Strength, Modulus) on the other. Improvements in both the materials used to make such films, and the process itself, can synergistically make blown films a more attractive commercial process. The inventors here have found desirable materials and methods of forming blown films.
Methods of cooling films extruded through a ring die have been discussed in U.S. Pat. No. 3,891,790. Other references of interest include: U.S. Pat. Nos. 7,687,580; 6,509,431; 6,355,757; 6,391,998; 6,417,281; 6,300,451; 6,114,457; 6,734,265; 6,147,180; 6,870,010; and 5,670,595; 3,568,252; WO 2007/067307; WO 2002/085954; US 2008/179780; US 2007/0260016; EP 0 544 098 A; and Guzman, et al., 56(5) AIChE Journal, 1325-1333 (2010).